The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board (PCB) attached to a disk drive base of the HDA. The head disk assembly includes at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The printed circuit board assembly includes electronics and firmware for controlling the rotation of the spindle and for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host.
The HSA typically includes an actuator, at least one head gimbal assembly (HGA), and a flex cable assembly. Each HGA includes a head for reading and writing data from and to the disk. In magnetic recording applications, the head typically includes an air bearing slider and a magnetic transducer that comprises a writer and a read element. In optical and magneto-optical recording applications, the head may include a mirror and an objective lens for focusing laser light on to an adjacent disk surface. The head is typically adhered to a suspension assembly that acts to preload the head against the surface of the disk.
During operation of the disk drive, the actuator must rotate to position the HGAs adjacent desired information tracks on the disk. The actuator typically includes a pivot-bearing cartridge to facilitate such rotational positioning. One or more actuator arms typically extends from the actuator body. An actuator coil is typically attached to the actuator opposite the actuator arms. The actuator coil is configured to interact with one or more fixed magnets in the HDA, typically a pair, to form a voice coil motor. The printed circuit board assembly provides and controls an electrical current that passes through the actuator coil and results in a torque being applied to the actuator.
There is competitive pressure to continually develop hard disk drives that can access data more quickly, and so techniques are continuously being developed to decrease access time. One potential technique to accomplish this is to increase the rotational accelerations with which the head stack assembly is pivoted to position the head over a desired track of information on the disk. Unfortunately, higher rotational accelerations and applied torques on the actuator may lead to increased excitation of certain undesired vibration modes of the actuator. Externally applied mechanical shocks can also excite such actuator vibration modes.
In particular, if there is inadequate frequency separation between an actuator system mode (e.g. the so-called butterfly modes and/or S-mode of the actuator system), with respect to an actuator arm mode (e.g. the actuator arm sway modes and/or torsion modes), then the useful bandwidth of effective actuator control may be undesirably reduced. Thus, there is a need in the art for ways to ensure adequate frequency separation between two or more of the aforementioned vibration modes of a disk drive actuator.